Granular cell dermatofibroma

Aims: To describe a series of five granular cell dermatofibromas as an unusual and rare manifestation of fibrohistiocytic tissue response. Methods and results: Five granular cell dermatofibromas were collected out of 136 tumours filed as granular cell tumours. Clinically, all lesions occurred on the shoulder or back of middle-aged adults (two women, three men), mostly with the clinical diagnosis of a fibrohistiocytic lesion. Histology revealed well-circumscribed, dermal to subcutaneous lesions dominated by periodic acid-Schiff (PAS) positive, granular cells. Acanthosis above, as well as storiform arrangement of spindle cells, sclerotic collagen and some interspersed lymphohistiocytic infiltrate at the periphery of the lesion, indicated the fibrohistiocytic origin. Lesions showed prominent reactivity with NK1C3 (CD57), as well as for macrophage markers KiM1p and KP1 (CD68), In contrast to classic Schwannian/neurogenic granular cell tumours, granular cell dermatofibromas were S100 protein negative, but showed variable reactivity for factor XIIIa (10-50%) in 4/5, for smooth muscle specific actin (10-50%) in 2/5 and with E9 (10-30%) in 3/5 lesions, Electron microscopy in one case revealed large pools of phago-lysosomes and variably sized glycogen granules in granular cells. Conclusion: Our series delineates granular cell dermatofibroma as a distinct clinicopathological variant of fibrohistiocytic tissue response which needs to be distinguished from other tumours with granular cell features.